this is my first post on the forums. Although I have found some similar topics, I cant the definite answer to the problem I am currently facing.

I have a 36x36x18 exo terra. First I have coated the backside and half of both side with a thin layer of black silicone. After three days of curing I made the foam + driftwood/cork bark background. I am close to finishing scraping and details. The foam I have used is ment for contact with drinking water.

Is it necessarily to coat all the scraped foam and little gaps between the wood and foam with silicone before gorilla glueing Hygrolon on it?

Should the Hygrolon be in touch with the water in the false bottom to ensure great moss growth on the background? Or is regular misting system gonna take care of it?

I don't believe you need to apply silicone to the foam before putting hygrolon on, but I don't use this method of building backgrounds, so someone else may have a different opinion. I think the silicone layer over the spray foam is mainly for cosmetics. You don't want the ugly (usually) yellow foam showing through in your build :-)

As for the hygolon for water transport, I think your tank is way too tall for hygrolon to be able to move water from the bottom of the tank to the top passively. You are going to need to mist it regularly to get moss to grow effectively (and maybe limit the air flow to some extent, but that will be a trial and error thing). I would not bother making sure the hygrolon touches the false bottom water. I would guess that it would only move water up a few inches but I don't have any data to back that up.

I have a 25" tall terrarium with a hygrolon background and it doesn't even wick water that high. It definitely wont wick your 36 inches. Misting the background helps, but the top of the terrarium still stays relatively dry; I can only get bulbophyllums and tillandsias to grow up there.

I have two 36x18x36 exos with hygrolon backgrounds and tall vines. A misting system is a must, I have a mistking and it works great. 4 nozzles in each tank and you have to be very patient with the growth. You’ll also need to most often enough depending on your ventilation as it dries out quickly. But overall my experience has been positive.